Valve device

ABSTRACT

A valve device for low-viscosity to high-viscosity fluids, especially for fluid plastic components of plastic mixtures consisting of one or more components, with a valve housing having a fluid inflow and a dosaging valve, which has a dosing nozzle that can optionally be closed or opened by a closing element, as well as a pressure control device which acts on the fluid in the fluid inflow.

BACKGROUND OF THE INVENTION

This application claims priority of German Application Serial No. 198 48358.9 filed Oct. 21, 1998, and PCT/DE99/07936 filed Oct. 19, 1999.

The invention relates to a valve device for low-viscosity tohigh-viscosity fluids, especially for fluid plastic components ofplastic mixtures consisting of one or more components. The deviceincludes a valve housing having a fluid inflow and a dosing valve. Thedosing valve has a dosing nozzle that can optionally be closed or openedby a closing element, as well as a pressure control device which acts onthe fluid in the fluid inflow.

Such valve devices are used particularly in the processing of plasticswith mixing heads, with the help of which the different plasticcomponents are mixed and then ejected as a processable plastic mixturethrough an outlet and, for example, are immediately moulded onto a partas a seal. The valve devices are arranged at the inlets of the mixinghead for the individual plastic components and serve to stop the supplyof a component when the dosing valve is closed. The valve devicesensure, when the dosing valve is opened, that the supplied component isintroduced into the mixing head not only with a constant volume flow,but also with a previously set, constant fluid pressure.

A valve device according to the above-mentioned type is known from DE-OS195 42 797. With this valve device, the pressure control device isformed essentially from a compression spring which is arranged in thehousing. The compression spring acts on the closing element which isformed as a valve needle. The compression spring pretension can beadjusted manually by adjusting an adjusting screw from the outside ofthe housing. The fluid pressure exerted by the spring on the nozzleneedle is in equilibrium with the fluid pressure. The fluid pressureacts on the frontal area of the nozzle needle which lies transversely toits shift direction. The pressure of the spring and the pressure exertedon the nozzle needle due to the fluid pressure are in equilibrium whenoperated, so that it is possible to control the fluid pressure in thefluid inflow by adjusting the spring pretension.

The '797 device is relatively complicated with regard to the adjustmentof the correct pressure ratios in the fluid inflow. The adjustment ofthe correct pressure ratios takes place manually from the outside of thehousing. Small adjustments of the adjusting screw result in relativelylarge pressure changes in the fluid, as the effective frontal area atthe nozzle needle, which transfers the spring force to the fluid, issmall due to its design. A particular disadvantage of the known deviceis that an operation at a constant fluid pressure, with the volume flowsupplied by a dosing pump, is only guaranteed as long as the nozzleneedle maintains its relative position in the valve housing when thevalve is open. If the cross section that is opened by the nozzle needleis reduced in this relative position, for example by deposits ofsolidified plastic components or other build-up of material, the nozzleneedle has to be opened further against the force of the spring, so asto maintain the steady cross section which is necessary for the constantvolume flow of the fluid. A small movement of the nozzle needle alreadyresults in a large change in the spring tension and the spring force, sothat the fluid pressure increases by a large amount, even when only asmall build-up of material occurs.

SUMMARY OF THE INVENTION

It is the object of the invention to avoid the aforementioneddisadvantages and to design a valve device of the above-mentioned typein such a way that a constant fluid pressure can be adjusted easily. Thefluid pressure is essentially independent of the position of the closingelement when the dosing valve is opened, and therefore is alsomaintained when contaminations occur at the nozzle cross section.

This object will be solved by means of the invention in that thepressure control device consists essentially of a pneumaticallypretensionable control membrane which acts on the closing element.

The use of a pneumatically or servo-pneumatically pretensionable controlmembrane, which replaces the compression spring used in the state of theart, allows a particularly simple pressure control of the fluid dosed bymeans of the device. The air pressure for changing the membranepretension can easily be adjusted automatically. By using a suitablepressure accumulator for the compressed air which pretentions themembrane, movements of the closing element which arise fromcontaminations at the nozzle outlet, result in practically no or only anegligible increase of pressure of compressed air and subsequently nochange of the fluid pressure. In particular, the design of the valvedevice according to the invention also facilitates its automatic controlby means of a computer-aided adjustment or change of the air pressureacting on the control membrane.

In a preferred design of the invention, there can also be arranged arecirculation valve in the valve housing in such a way that the dosingvalve is optionally opened for the supply of fluid to a processingdevice or the recirculation valve is opened for the return of the fluidto a storage vessel. With this configuration, the supplied fluid iseither supplied to for example the mixing head by the dosing valve ofthe processing device, or is conveyed in the cycle back to the storagevessel by the recirculation valve. The compact unit of dosing andrecirculation valve in a common housing avoids difficulties in thestarting phase of the subsequent processing device, as this is alwayscompletely filled due to the circulation of fluid in the cycle, andfresh fluid is always added as soon as the dosing valve opens.

The control membrane is preferably part of a pneumatically chargeablepressure control chamber and acts on the closing element designed as avalve needle by means of a plunger which can be moved in the housing.The pressure control chamber thereby forms the pressure storage for thecompressed air which acts on the fluid in the fluid inflow by means ofthe control membrane. The force exerted by the compressed air istransferred to the valve needle by means of the plunger essentiallywithout friction losses. The pressure control device is preferablyarranged separately from the fluid inflow by means of a shut-offmembrane, whereby it is ensured that no fluid can reach the sensitivecontrol membrane. The shut-off membrane is preferably arranged betweenthe closing element and the plunger, so that the plunger is alsoseparated from the fluid inflow and that its very accurate, mainlyfrictionless mounting in the valve housing is not adversely affected bythe entry of fluid.

The plunger can be charged by the control membrane by means of apressure pin mounted at the control membrane, which is supported at theplunger by means of a ball bearing element. The ball bearing element,which preferably consists simply of a single ball, effects an evencentral transfer of the forces acting between the plunger and thepressure pin essentially without friction losses, so that an exactpressure balance can take place between the air pressure at the controlmembrane and the fluid pressure in the fluid inflow.

The closing element is preferably pretensioned in the direction of theplunger by means of a spring which is supported in the housing. When thedosing valve is opened, the spring draws the dosing element in thedosing nozzle back at least to such an extent that the fluid pressure ofthe supplied fluid can act on the closing element. The closing elementof the dosing valve can be moved by an actuating device for closing oropening the dosing nozzle. The actuating device consists in aparticularly advantageous manner essentially of an actuating lever thatcan be actuated in the actuating cylinder. The actuating lever ismounted pivotally in the housing and acts on the closing element or thepressure cylinder against the spring. In particular, with theparticularly advantageous design of the invention, in which therecirculation valve and the dosing valve are constructed essentially inthe same way, it is possible that the dosing valve and the recirculationvalve or their closing elements can be actuated by a common actuatinglever.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention result from thefollowing description and the drawing, wherein a preferred embodiment ofthe invention is explained in detail. It shows:

FIG. 1 is a flow sheet for illustrating the preferred use of a valvedevice according to the invention;

FIG. 2 is a valve device according to the invention in a top view;

FIG. 3 is the object of FIG. 2 in a section along line III—III with anopened dosing valve; and

FIG. 4 is the object of FIG. 2 in a section along line IV—IV with anopened recirculation valve.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a flow sheet of a part of a plastics processing device 10with a mixing container 11 for a plastic component 12 to be processed,which is either supplied to a mixing head for plastic mixtures, notshown in detail, by means of a dosing valve 15 via a conduit 13 and avalve device 14, or is pumped back to the storage vessel 11 in the cyclevia a second conduit 17 by means of a recirculation valve 16.

The valve device 14 is depicted in FIGS. 2-4. It consists essentially ofa valve housing 18, in which are arranged the dosing valve 15 and therecirculation valve 16. A fluid inflow 20 and a return connector 21 forconnecting the conduits 13 or 17 are provided at the upper side 19 ofthe housing, whereas a fluid outlet 22 is provided at the lower end ofthe housing, from which the plastic fluid is injected into the mixinghead of the plastic processing device.

The dosing valve 15 and the recirculation valve 16 are essentiallyconstructed in the same way, so that only the dosing valve will bedescribed in detail. It consists essentially of a valve needle 23 whichforms a closing element for the fluid outlet. The valve needle 23 isreceived axially moveable in a channel 24 which is arranged in theoutlet 22, and which closes the opening 26 of the outlet when its tip 25is moved in a forward position (to the left in the drawing) and opens itin the pushed-back position. To facilitate the opening of the valveneedle 23, there is arranged a small helical spring 27 in the channel,which is pretensioned when the valve is closed and then endeavours tomove the needle into the open position of the valve.

The valve needle 23 is mounted to a shut-off membrane 29 with its headat the back (to the right in the drawing) which separates the channels30 for the fluid inflow to the outlet 22 or for the return of the othervalve units. The shut-off membrane is clamped between a part 18 e of thevalve housing and a cylinder element 31, which is threaded therein andcan extend in the axial direction of the valve needle to such an extent,that it does not prevent or limit a movement of the needle 23 from itsclosed to its opened position.

On the other side of the shut-off membrane 29, which does not carry anyfluid, a plunger 32 is moveably arranged in the cylinder element 31. Thecylinder element is adjacent to the plunger's front side 33 by means ofthe intermediate shut-off membrane 29 against the head 28 of the valveneedle. A central bore 35 is provided at the back side 34 of the plunger32. The central bore receives a pressure pin 36, which is supported onthe base 37 of the bore by means of a ball 38 at the plunger.

The pressure pin 36 is provided with a clamping device 39 for a controlmembrane 40 at its rear end. The control membrane consists of a firstclamping plate 41 and a second clamping plate 43 which is threaded tothe first plate by means of a central screw 42. The control membrane 40is clamped between the first and second plates in a sealing manner. Thecontrol membrane is part of a pneumatically chargeable pressure chamber44. At the edge, the pressure chamber is clamped in an airtight mannerbetween a part 18 b of the valve housing and a pressure chamber lid 45.The pressure chamber comprises a connector for compressed air, not shownin detail, which is controlled by means of an external supply ofcompressed air.

The recirculation valve is constructed essentially identical to thedosing valve, but the valve needle 23′ of the recirculation valve 16 isshorter than that of the dosing valve. The recirculation valve serves toconnect the fluid inflow 20 in the open nozzle needle position to thereturn 21. Alternatively, the recirculation valve can stop a fluidreturn along the second conduit 17 in the closed position of the valve,so as to eject the entire supplied fluid into the mixing chamber bymeans of the dosing valve which is then opened.

The switching of the two valves in the housing is effected by means of acommon switching device. The switching device can be pivoted essentiallyby means of a switching lever 46 which is mounted pivotally in thehousing. The switching lever can be pivoted by an actuating cylinder 47which is arranged in the upper part of the valve housing 18, and therebymoves the valves simultaneously in such a way that one valve will beclosed when the other valve will be opened. The arrangement is in such away that the switching lever presses, when the recirculation valve isclosed. When the dosing valve is opened, as shown in FIG. 3, theactuating lever 48 which surrounds the plunger of the recirculationvalve 16 lying above the pivot axis 49, presses the valve needle 23′ ofthe recirculation valve into the closed position, while the lower end ofthe switching lever 46 has no contact with the plunger of the dosingvalve, so that the valve needle is pressed back into the housing bymeans of the spring 27 and opens the opening 26. When switching overinto the recirculation mode as shown in FIG. 4, the pressure in theactuating cylinder 47 is reduced, whereby an actuating spring 50 turnsthe switching lever 46, whereby the actuating lever 48 disengages fromthe plunger of the recirculation valve on the one hand and opens thevalve needle 23′, and on the other hand the switching lever presses theplunger of the dosing valve forward with its lower end (to the left inthe drawing) and closes the valve.

It is obvious that, when the dosing valve 15 is opened, neither thepressure spring nor the switching lever act on the nozzle needle or theplunger, and the closing element is supported at the control membrane bymeans of the plunger and the pressure pin practically unaffected bymechanical influences. This also means that the pressure of the fluidflowing through the valve device is in equilibrium with the pneumaticpressure in the pressure chamber 44, that is, mainly unaffected by theposition of the nozzle needle and the piston in the valve housing, asmovement of the plunger in the axial direction and thereby a squeezingof the control membrane into the pressure chamber only effects a smallchange in volume, and the pressure increase, which theoretically takesplace is so small that it can be neglected as being negligibly small.The theoretical pressure increase in the pressure chamber charged withair decreases with the increase of the entire volume of the cycle ofcompressed air, into which the pressure chamber is bound. As the airpressure in the pressure chamber is controlled automatically, the volumeof the pressure chamber is in these cases without particular importancefor the pressure increase in the air and therefore in the fluid.

This particular design makes it possible with the valve device accordingto the invention to ensure a constant fluid pressure in the suppliedplastic component independently of the position of the nozzle needle inthe housing. If soilings of the dosing valve or of the recirculationvalve should occur in the region of their openings 26, which reduce thecross section in this region, the nozzle needle can move furtherbackwards, whereby the original cross section is reproduced without anincrease in the fluid pressure. The fluid pressure can be changed veryeasily and accurately by changing the air pressure in the pressurechamber, so that the valve device according to the invention is verysuitable for an automatic control or adjustment of the fluid pressure,which can take place by means of a suitable control device, for examplea control (SPS), which can be programmed in a memory.

The mechanical coupling of both valves by means of the common controllever guarantees that both valves are always actuated at the same time.When one valve is opened, the other valve is always in its closedposition, so that a wrong operation (for example two closed valves) issafely excluded.

Having thus described the invention, it is claimed:
 1. A valve devicefor low-viscosity to high-viscosity fluids, in particular for fluidplastic components of plastic mixtures having single or multiplecomponents, with a valve housing having a fluid inflow and a dosingvalve, which comprises a dosing nozzle that can optionally be closed oropened by means of a closing element, as well as a pressure controldevice which influences said fluid in said fluid inflow, which consistsessentially of a pneumatically pretensionable control membrane whichacts on said closing element, wherein said pressure control device isarranged separately from said fluid inflow or the passages holding saidfluid in said valve housing by means of a shut-off membrane, saidcontrol membrane is part of a pneumatically chargeable pressure controlchamber and acts on said closing element formed as a valve needle bymeans of a plunger which is moveable in said housing, said plunger ischarged by said control membrane by means of a pressure pin which ismounted on said control membrane, said pin is supported at said plungerby means of a ball bearing element, said closing element is pretensionedby a spring which is supported in said housing in the direction of saidplunger, said closing element of said dosing valve can be moved by meansof an actuating device for closing or opening said dosing nozzle, saidactuating device essentially consists of a control lever which can beactuated by an actuating cylinder, which is mounted pivotally in saidhousing, which acts on said closing element or a plunger against saidspring, said dosing valve and said recirculation valve or theirrespective closing elements can be actuated by said control lever. 2.The valve device of claim 1, wherein a recirculation valve isadditionally arranged in said valve housing, so that said dosing valveis optionally opened for the supply of fluid to a processing device orsaid recirculation valve is opened for the return of said fluid to astorage vessel.
 3. The valve device of claim 2, wherein saidrecirculation valve and said dosing valve are constructed in essentiallythe same way.
 4. The valve device of claim 1, wherein said shut-offmembrane is arranged between said closing element and said plunger.